1. Field of the Invention
The present invention relates to a high-frequency module that includes a module substrate on which a filter component is mounted.
2. Description of the Related Art
In the related art, high-frequency modules equipped with filters have been provided. For example, a filter 500 illustrated in FIG. 12 is mounted in a high-frequency module (for example, refer to Japanese Unexamined Patent Application Publication No. 2012-109818). The filter 500 includes a filter section 503, which is connected between a first terminal 501 and a second terminal 502, and a path 504 that is connected in parallel with the filter section 503. Therefore, a signal path, along which a high frequency (radio frequency (RF)) signal input to the first terminal 501 passes, splits into the path of the filter section 503 and the path 504, and consequently, when an RF signal is input to the first terminal 501, a first signal 505 passes through the filter section 503 and a second signal 506 passes along the path 504. Then, an RF signal which results from the first signal 505, which has passed through the filter section 503, and the second signal 506, which has passed along the path 504, being combined with each other is output from the second terminal 502.
The filter section 503 preferably includes a band pass filter in which a prescribed pass band is set. The filter section 503 allows an RF signal of the pass band to pass therethrough and attenuates RF signals that are outside the pass band. However, it may not be possible to attenuate RF signals outside the pass band to a desired value using just the filter section 503. Therefore, the path 504 is provided with a correction circuit formed of an inductor and a capacitor. The impedance of the path 504 is set such that the second signal 506 that passes along the path 504 and corresponds to a frequency band outside the pass band of the filter section 503 and the first signal 505 that passes through the filter section 503 and which it is desired to further attenuate opposite phases from each other in a frequency band outside the pass band of the filter section 503 and such that the amplitude of the first signal 505 and the amplitude of the second signal 506 are the same as each other in a frequency band outside the pass band of the filter section 503.
Therefore, the first signal 505 that passes through the filter section 503 and the second signal 506 that passes along the path 504 cancel each other out in a frequency band outside the pass band of the filter section 503 at a connection point between a signal line on the output side of the filter section 503 and a signal line on the output side of the path 504, and therefore an RF signal of a frequency band outside the pass band output from the second terminal 502 is attenuated. Therefore, the attenuation characteristics of the filter 500 for an RF signal outside the pass band of the filter 500 are improved. In addition, in the case where another filter, which preferably includes a band pass filter in which a pass band is set that is different from that of the filter 500, is arranged adjacent to the filter 500, the occurrence of a situation in which an RF signal outside the pass band of the filter 500 is output from the second terminal 502 and flows around to the other filter is suppressed. Therefore, it is possible to improve the isolation characteristics between the filter 500 and the other filter that are arranged adjacent to each other.
In the filter 500 of the related art described above, in order to improve the attenuation characteristics for an RF signal outside the prescribed pass band, the path 504 has to be provided separately from the filter section 503, the path 504 being provided with a correction circuit (circuit elements such as an inductor, a capacitor and so on) for generating an RF signal having the opposite phase to an RF signal outside the pass band that passes through the filter section 503. Therefore, there is a problem in that the filter 500 is increased in size and a high-frequency module that includes the filter 500 is increased in size.